Since an electrostatic rotary atomizing coating machine can finely particulate a coating material uniformly and conduct coating uniformly and at high quality, it is generally used also for coating of automobiles requiring stringent coating quality.
In the coating line for such automobiles, since automobile bodies as works are conveyed successively irrespective of coating colors, it is adapted such that coating materials of a plurality of colors can be coated under color change by a single coating machine so that respective works can be coated with designated coating colors.
By the way, in a case of color-change coating from a coating material of a preceding color to a coating material of a succeeding color, since color mixing is caused when coating is applied with the coating material of the succeeding color to result in coating failure unless the coating material of the preceding color remaining in the coating machine is cleaned, cleaning for color-change is conducted on every time.
Since a thinner and air are alternately supplied to a coating machine upon conducting cleaning for color-change and the coating material remaining in the coating machine and the coating material of a preceding color deposited to a rotary atomizing head are removed thoroughly, color mixing does not occur.
In this case, a hopper used for cleaning a coating machine is disposed and the coating machine is cleaned in the inside thereof for preventing the residual toner or the thinner from being sprayed as coating mists from the rotary atomizing head, scattering and depositing to works.
FIG. 7 shows such an existent cleaning hopper 31, in which an opening 33 for entering an rotary atomizing head B of a coating machine T, is formed to the upper surface of a hopper housing 32, and a residual coating material and a thinner are sprayed in the hopper housing 32 upon cleaning the coating machine T by supplying the thinner.
[Patent Document 1] JP-A No. 2000-189849
In this case, since particles of the residual coating material particulated by the rotary atomizing coating machine are extremely fine and extremely light, they tend to undergo the effect of a surrounding airstream.
Particularly, it has been well known that when the rotary atomizing head B is rotated at a high speed, an airstream therearound is disturbed and the coating material whirling up through a gap G between the coating machine T and the opening 33.
Accordingly, a shaping air SA is sprayed from the coating machine T for preventing sprayed coating material particles from whirling up during cleaning.
However, use of the shaping air SA results in a loss of energy by so much, as well as the shaping air SA generates another airstream depending on the case and the coating material particles sometimes whirl up under the effect thereof.
In view of the above, the present inventors have analyzed the airstream formed at the periphery of the coating machine in a case of not using the shaping air.
FIG. 8 is a model of an airstream and it was found that when air around a rotary atomizing head B is rotated into a rotational flow Q31 by the rotation of the rotary atomizing head B, a negative pressure zone 34 is formed below the rotary atomizing head B by the centrifugal force thereof and a primary ascending airstream Q32 is formed from below to above toward the negative pressure zone 34, air therearound forms a secondary ascending airstream Q33 under the effect of the primary airstream Q32 to form an upward vortex flow Q34 while rotating along the coating machine T undergoing the effect of the rotational flow Q31, and the vortex flow Q34 causes the coating material particles to whirl up.
Accordingly, if it is possible to eliminate the vortex flow Q34, since airstream flowing from the inside of the hopper housing 32 outwardly passing through the gap G between the coating machine T and the opening 33 is eliminated, it is considered that upward whirling of the coating material particles is to be eliminated.